Tinkering with code and algorithms for fun
function parseInput(input) {
let [rules, tickets] = input.split("\n\nnearby tickets:\n");
let yourTicket;
[rules, yourTicket] = rules.split("\n\nyour ticket:\n");
rules = rules.split('\n').map(rule => {
let [name, ranges] = rule.split(": ");
ranges = ranges.split(" or ").map(range => range.split("-").map(nr => +nr));
return { name, ranges };
});
yourTicket = yourTicket.split(",").map(v => +v);
tickets = tickets.split("\n").map(ticket => ticket.split(",").map(v => +v));
return { rules, yourTicket, tickets };
}
testInput = parseInput(testInput_text)
input = parseInput(input_text)
function q1(input) {
const invalid_vals = [];
const valid_tickets = [];
const { rules, tickets } = input;
for (const ticket of tickets) {
let valid_ticket = true;
for (const val of ticket) {
let valid_rule = false;
for (const rule of rules) {
let valid_range = false;
for (const range of rule.ranges) {
if (val >= range[0] && val <= range[1]) {
valid_range = true;
break;
}
}
if (valid_range) {
valid_rule = true;
break;
}
}
if (!valid_rule) {
invalid_vals.push(val);
valid_ticket = false;
}
}
if (valid_ticket) valid_tickets.push(ticket);
}
let sum = 0;
for (const val of invalid_vals) sum += val;
return { valid_tickets, invalid_vals, sum };
}
testAnswer1 = q1(testInput)
answer1 = q1(input)
q2(testInput2)
function q2(input) {
const t0 = performance.now();
const { rules, yourTicket, tickets } = input;
let sieve = rules.map(rule => {
const possibleColumns = new Set();
return { name: rule.name, possibleColumns };
});
// to clarify which loop is which
const columns = rules.length;
for (let i = 0; i < rules.length; i++) {
const { possibleColumns } = sieve[i];
const rule = rules[i];
for (let j = 0; j < columns; j++) {
let always_valid = true;
for (const ticket of tickets) {
const col_val = ticket[j];
let valid = false;
for (const range of rule.ranges) {
valid = valid || (col_val >= range[0] && col_val <= range[1]);
}
always_valid = always_valid && valid;
if (!always_valid) break;
}
if (always_valid) possibleColumns.add(j);
}
}
let identified = [];
for (let i = 0; i < rules.length; i++) {
// put rule with fewest possible columns at the end
sieve.sort((a, b) => b.possibleColumns.size - a.possibleColumns.size);
// let's hope that there's always at least one rule with
// only one possible column after every loop
const lastRule = sieve.pop();
if (lastRule.possibleColumns.size === 1) {
identified.push(lastRule);
for (const column of lastRule.possibleColumns.values()) {
for (const rule of sieve) {
rule.possibleColumns.delete(column);
}
}
} else {
return "gotta think of a different strategy, chief";
}
}
sieve = identified;
for (const { name, possibleColumns } of sieve) {
for (const column of possibleColumns.values()) {
for (const rule of rules) {
if (rule.name === name) {
rule.column = column;
break;
}
}
}
}
let answer = 1;
for (const rule of rules) {
if (!rule.name.startsWith("departure")) continue;
answer *= yourTicket[rule.column];
}
return { rules, yourTicket, sieve, answer, time: performance.now() - t0 };
}
q2(input2)
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